In image forming apparatuses, such as printers, toner images formed on paper are fixed on the paper by fixing devices. In order to fix toner images on paper by heat and pressure at the fixing devices, the image forming apparatuses detect temperatures of heating rollers by temperature detection elements and control heaters in the heating rollers at optimum temperatures (target temperatures).
Accordingly, it becomes difficult to control the temperature due to an abnormality in the temperature detection element. Patent Document 1 discloses detecting abnormality in a temperature detection element. Patent Document 1 discloses an abnormality detection method for detecting an abnormality in a temperature detection element by, in the case where although the temperature detection element itself remains normal a temperature becomes impossible to be detected normally, monitoring outputs from plural temperature detection elements arranged on an outer periphery of a heating roller at intervals, and comparing temperature rise rates of the temperature detection elements with each other.